Preparation and use of plant embryo explants for transformation

ABSTRACT

The present invention relates to excision of explant material comprising meristematic tissue from seeds, and storage of such material prior to subsequent use in plant tissue culture and genetic transformation. Methods for tissue preparation, storage, and transformation are disclosed, as is transformable meristem tissue produced by such methods, and apparati for tissue preparation.

This application claims the priority of U.S. Provisional applicationSer. No. 60/894,096, filed Mar. 9, 2007, and 60/915,066, filed Apr. 30,2007, the entire disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates generally to methods for preparing and storingembryonic plant tissue and its subsequent use in regeneration andtransformation. The invention relates generally to methods for preparingand storing embryonic plant tissue directly from dry seed and itssubsequent use in regeneration and transformation. The resulting novelexplant is storable and can germinate and or be transformed whenappropriate conditions are provided.

2. Description of Related Art

Transformed plants may be obtained by directly treating meristematictissue of a plant embryo (e.g. U.S. Pat. No. 6,384,301). Themeristematic tissue contains formative plant cells that differentiate toproduce multiple plant structures including stem, roots, leaves, germline tissue, and seeds. Plant embryos may be treated and selected orscreened to determine which of those treated embryos have incorporatedthe new genetic information into germ line tissue. U.S. Pat. Nos.6,384,301 and 7,002,058 and U.S. Publication 20060059589 describemethods of genetically transforming soybeans (Glycine max) usingbacterial-mediated gene transfer directly on the meristematic cells ofsoybean embryos.

In typical soybean transformation procedures, seeds are hydrated/imbibedto soften the seed coat and allow for or extraction of the explanttissue. After hydration the embryo or embryonic tissue is excised fromseed. When meristems are used as the explant, primary leaf tissue may beremoved to expose the meristem of the soybean embryo. Considerableeffort is involved in excising the embryos, transferring the geneticmaterial into the embryos, and culturing the embryos. Processing cancause damage to the explant tissue, which negatively impacts subsequenttransformation and regeneration steps. It is thus important to reducedamage to the explant tissue that could result in transformation and/orregeneration effort being applied to non-viable tissue.

The excision of plant embryos is often therefore performed by hand. Inthis process, surface sterilized seeds are aseptically handled one at atime with gloved hands. The explant is then carefully excised. In thecase of meristems, the seeds are carefully oriented in a manner as toeject the seed coat with applied force and then the embryonic leaves(cotyledons) are removed near the primary meristem to leave the seedembryo containing meristematic tissue. Even the careful handling ofindividual seeds, however, results in less than desirable recovery ofviable embryos, and may be less than 70% even with high quality seeds.

Bacterial contamination of embryos after excision is also a significantconcern. The increased handling to preserve higher viability andrecovery of explants also increases the likelihood of destructivecontamination (which will manifest itself in subsequent processingsteps). Such contamination can result in significant loss, as a singlecontaminated explant will contaminate other samples during tissueculture. This causes loss of yield and/or transformation frequency, andeventually transformation efficiency. Moreover, the manual excision isextremely labor intensive, time-consuming, and stands as a barrier to ascaling up of the transformation process in which many plants musttypically be treated to yield desired results.

In addition, the current processes are limited because the harvestedexplant must be moved quickly into the subsequent steps oftransformation, or viability is lost. Typically, once an explant isharvested (e.g. U. S. Patent Application Publication 20050005321 andcorresponding PCT Publication WO 2005/000471), it is placed on media andsubjected to co-culture with transforming bacteria within hours of beingremoved. Thus, anytime transformations are to be performed, it isnecessary to first prepare all of the explants that will be needed sothey are ready to immediately move into an incubation or transformationprocess. This timing can be very complicated and inflexible,particularly if sudden demands arise and explants cannot be prepared intime. Clearly, the lack of an ability to store such explants for morethan a few hours is a major deficiency in the art.

There remains a great need for processes that can increase theavailability of transformable embryos without unacceptably increasingtotal costs and/or timelines of explant preparation for transformation.The ability to store excised meristematic tissue (explant) for later usein particular has been lacking. Such methods would substantiallyincrease the availability of transformable embryos, and allow efficientplanning and execution of large-scale transformation studies. Suchmethods should enable explant storage to meet demands created duringpeak operational hours or during inadvertent disruptions in theproduction line and shipping of explants, for example, to differentsites for maintaining production runs. Further, the use of dry embryoexplants (artificial seeds) for transformation is not known in the artdue to common wisdom in the art to use “wet” explants fortransformation.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a seed explant having a specifiedmoisture content. In one embodiment, an explant may comprise an internalmoisture content of from about 3% to about 20%. In a furtherembodiments, an explant provided herein may be defined as a storable,substantially intact embryo axis containing at least some meristemtissue that is extracted from a seed with an internal moisture asspecified herein, for example, from about 3% to about 20%.

In another aspect, the invention comprises a method for producingobtaining a plant comprising the steps of: (a) obtaining a dry plantseed; and (b) preparing an explant from the plant seed under conditionswherein the explant does not germinate and remains viable and competentfor germination and or genetic transformation. The plant seed may be asoybean, canola, corn, cotton, onion, pepper, tomato, cucurbit, rice, orwheat seed.

In certain embodiments, the explant comprises a substantially intactseed modified to expose at least a first transformable cell of the seed.In other embodiments, the method for preparing the explant may comprisedrilling at least a first aperture in the seed, or nicking the seed. Theseed or explant comprises meristematic tissue.

In certain embodiments the method may further comprise the step of (c)transforming at least a first cell of the explant with a selected DNA,and (d) regenerating a transgenic plant from said cell, wherein theregenerated plant is stably transformed with the selected DNA.Regenerating may be performed at a temperature of up to about 35° C. Theexplant may further comprise meristematic tissue, for instance anembryonic meristem. In one embodiment, a plant may be regeneratedwithout the use of one or more plant growth regulators such as to alterthe development of the explant.

In other embodiments, the method may comprise storing the explant priorto step (c) or (d) under conditions wherein the explant does notgerminate. In yet other embodiments, the seed or explant may bedehydrated prior to or after preparing the explant. A transformable andregenerable explant produced by the method is also an aspect of theinvention.

In certain embodiments, the conditions in step (a) or (b) may comprise aseed or explant internal moisture content of from about 3% to about 25%.In particular embodiments the conditions in step (a) or (b) may comprisea seed or explant moisture content of from about 4% to about 16%. Incertain embodiments, the method may be defined as comprising reducingthe moisture content of the plant seed and/or the explant prior to step(c). In other embodiments, the method may further be defined ascomprising increasing the moisture content of the explant prior to,concurrently with, and/or after step (d).

Further, the methods may be defined as ones wherein step (a) and/or step(b) is performed in the absence of a liquid. Alternatively, the methodsmay be defined as ones wherein step (a) and/or step (b) is performed inthe presence of a liquid. In yet other embodiments, the methods may bedefined as ones wherein step (a) and step (b) are performed in theabsence of a liquid. The conditions in step (a) or (b) may comprise atemperature of between about −80° C. and about 60° C. In particularembodiments, the temperature may be between about −20° C. and about 40°C.

In other embodiments, the method may be defined as one wherein step (b)is further defined as comprising obtaining a plurality of explants fromplant seeds and selecting an explant from the plurality based on acharacteristic associated with the ability to transform the explantand/or regenerate a plant from the explant. In particular embodiments,the characteristic is selected from the group consisting of color, size,shape, density, proximate analysis, carbohydrate content, proteincontent, fat content, volatile content, fibre (ash) content, moisturecontent, viability, germplasm, intactness, pathogen presence, andoptical characteristics.

In certain embodiments, the method may be further defined as comprisingsanitizing the plant seed and/or the explant prior to or concurrentlywith step (c). The method may further comprise priming the seed bycontacting the seed with an aqueous solution. The aqueous solution maycomprise a disinfectant such as bleach or alcohol. The method mayfurther be defined as comprising disinfecting the plant seed and/or theexplant prior to step (c). In certain embodiments, the method maycomprise disinfecting the explant, wherein disinfecting comprisesapplication of a disinfectant selected from the group consisting ofbleach, alcohol (e.g. ethanol), ozone, chlorine gas, ultraviolet light,temperatures of −20° C. or lower, and exposure to a temperature higherthan 40° C. or 50° C.

The method for obtaining an explant from a seed may be automated. Incertain embodiments, the method comprises an automated process in whichthe plant seed is oriented as it passes through a mechanical separatorto provide a substantially uniform output of regenerable meristematicplant tissue. The method may be performed on bulk seed using the forcegenerated with opposing rollers, such as illustrated in FIG. 6, forexample, as well as on singulated seed such as illustrated in FIGS. 2-5,for example.

In some embodiments, the transformation method may be carried out bybacterially-mediated transformation, or by microprojectile bombardment.Explant transformation may be carried out prior to, or subsequent to,explant disinfection. The method may be performed wherein the transgenicplant is regenerated without producing a callus tissue culture, byorganogenesis or by direct meristem transformation and subsequent shootgrowth.

Further, the method may comprise storing the explant for from about 1hour to about 2 years prior to step (c) or step (d). In certainembodiments the method may comprise storing the explant for from about 1hour to about 24 hours. The explant may be hydrated or pre-culturedafter storage.

Another aspect of the invention comprises an apparatus for preparationof transformable embryonic plant tissue from singulated seed comprising:(a) a holder for a singulated seed; (b) a means for applying a force tothe seed being held so as to divide the seed into separate cotyledons,seed coat and embryonic tissue. The apparatus may further comprise: (c)a means for separating the embryonic tissue from the seed coat andcotyledons and (d) a means for cleaning and/or sterilizing the tissue.FIGS. 2-5 illustrate an apparatus for preparation of transformableembryonic plant tissue from singulated seed. As shown in FIG. 3, theapparatus (1) comprises a holder (2) for the singulated seed (16). Asshown in FIG. 2, the holder (2) comprises an upper and lower seedfixture (3, 4); and means for applying force to the seed (16) at a shearforce point or plane (5), to divide the seed (16) into separatecotyledons, seed coat, and embryonic tissue. The holder may comprisevacuum cups (6) that maintain the position of the seed (16) whileapplying a shear force to it. FIG. 4 illustrates an alternativeembodiment of the holder (2), wherein serrated knurled posts (7)maintain the position of the seed (16) while applying shear force. Thevacuum cups or serrated posts turn in opposite directions, generatingthe force which results in division of the seed (16) at or near theshear force point (5). The apparatus further comprises vacuum generators(8) or similar means for removing components of a sheared singulatedseed from the vicinity of the holder (2), allowing the next seed to beplaced therein.

FIG. 6 illustrates a method useful for bulk separation of embryonicmeristem tissues from cotyledon tissue and seed coat tissues. Sheer isgenerated between rollers. In this example, one is metal and one is anelastomer. Dry seed is passed between these two rollers at a gap settingappropriate for the seed type, and sheer is applied such that the seedis split and seed coats and cotyledon parts can be further separatedfrom the desired meristem containing embryo axis, for example, utilizingadjustable air flow and properly sized screens or the like.

FIG. 7 illustrates an apparatus for separating embryonic tissue fromcotyledon, seed coat, or other debris, and cleaning the tissue. As shownin the separator (13) of FIG. 7, sterile air flows through a manifold(9) into an explant delivery and recovery chamber (10). Air flow forcesthe plant material comprising embryonic tissue into an explant freeflight area (11), where materials are separated. The apparatus mayfurther comprise an explant excluding chamber (12) to prevent explantloss but allow passage of dust and airflow out of the separator (13),and a means for static removal such as an ion generator (17). FIG. 8illustrates an alternative embodiment of the separator (13), comprisingcharged plates (14) to collect dust, mold spores, or the like. FIG. 9illustrates yet another embodiment of a separator, further comprising ameans for sterilizing the tissue. As shown in FIG. 9, a sterilizingmeans such as germicidal UV lamps (15) may be placed within theseparator (13), such as within the explant free flight area (11), tosterilize the explant tissue.

Still yet another aspect of the invention is a method for preparingtransformable and regenerable explant material comprising meristematictissue from a singulated seed, comprising: a) subjecting a singulatedseed that comprises a seed coat, cotyledon tissue, and meristematictissue to a force sufficient to fracture the seed; and b) separating themeristematic tissue from the seed coat and optionally the cotyledontissue, wherein the method is mechanized. A transgenic plant produced bythis method, wherein the method further comprises transforming andregenerating the explant material to produce a transgenic plant, is alsoan aspect of the invention. In certain embodiments the plant may be asoybean, cotton, onion, pepper, rice, wheat, cucurbit, canola or cornplant.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are part of the present specification and areincluded to further demonstrate certain aspects of the presentinvention. The invention may be better understood by reference to thedrawings in combination with the detailed description of specificembodiments presented herein.

FIG. 1: Yield of meristematic soybean explants after subjecting seeds toautomated excision.

FIG. 2: Partial perspective view of apparatus (FIG. 3) for highthroughput explant excision from single seed using vacuum cups.

FIG. 3: Simplified representation of an apparatus with vacuum cups forthe excision of explant material from singulated seed.

FIG. 4: Partial perspective view of apparatus (FIG. 5) for highthroughput explant excision from single seed using serrated seed holder.

FIG. 5: Simplified representation of an apparatus with serrated seedholder for the excision of explant material from singulated seed.

FIG. 6: Flow chart showing principal steps of the Excision Process.

FIG. 7: Dry Explant Sanitizer embodiment 1.

FIG. 8: Dry Explant Sanitizer embodiment 2.

FIG. 9: Dry Explant Sanitizer embodiment 3.

FIG. 10: Closeup view of an embodiment of a “stacked” apparatus forobtaining explant tissue from seed.

FIG. 11: Embodiment of a “stacked” apparatus for obtaining explanttissue from seed.

DETAILED DESCRIPTION OF THE INVENTION

The following is a detailed description of the invention provided to aidthose skilled in the art in practicing the present invention. Those ofordinary skill in the art may make modifications and variations in theembodiments described herein without departing from the spirit or scopeof the present invention.

The invention provides methods and compositions for preparing andrecovering and storing explants, for instance, using mechanization andautomation. Fluid can be used to move explants and separate desirableexplants from debris during mechanized handling of seeds and embryonictissue, including compressed air, other gases, and liquids. Wet or dryexcision of plant embryos to yield transformable meristematic tissue maybe performed, followed by immediate use in transformation methods.Alternatively, wet or dry excised embryos may be subsequently dried andstored for later transformation or other use and dry excised embryos maybe stored as such or after drying them further depending upon theirmoisture content at the time of excision.

Flexibility of plant transformation methods is increased by redefiningthe storage product from seed to transformation-ready explant. Explantpreparation can occur at off-peak times and days, and explants storedfor later use, greatly enhancing the efficiency of the overalltransformation process. Advancements in excision, processing, explantisolation and storage, and manipulation make this process much morelabor efficient and well suited for high volume, high-throughputtransformation needs. Methods for the manipulation of the moisturecontent of the seed to adjust seed shattering characteristics andsubsequent seed and explant vigor and process yield are also provided bythe invention. Transformable embryos and meristems produced by thedescribed methods are further an embodiment of the invention,

In one embodiment, an explant prepared in accordance with the inventionmay be defined as having an internal moisture of about 4-25%, includingabout 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 21, 22,23, 24, and 25% internal moisture, and specifically including all rangesderivable between any two such values. In particular embodiments, seedsfrom which explants are to be prepared may be harvested at apredetermined internal moisture suitable for isolating transformablematerial therefrom. In certain non-limiting embodiments, seeds fromwhich explants are obtained may be defined as having an internalmoisture of about 3-25%, including about 3, 4, 5, 6, 7, 8, 9, 10, 11,12, 13, 14, 16, 17, 18, 19, 20, 21, 22, 23, 24, and 25% internalmoisture, and specifically including all ranges derivable between anytwo such values, such as, for example, from about 4% to 16%. In certainembodiments, brittleness of seeds may be altered by manipulatingmoisture content, allowing for efficient splitting of seeds andpreparation of explants. For instance, an internal moisture content suchas 3% to 7% may be advantageous. Seeds may be held at such moisturecontents or any other moisture content yielding stable storageconditions (and transformable explants) prior to use. The seeds incertain embodiments may be soybean or cotton seeds, and may also be,without limitation, corn, canola, onion, pepper, tomato, cucurbit, rice,common bean, peanut, maize, wheat, or rapeseed seeds.

Dry explants may be used that have been excised from seed under lowmoisture conditions, and may be prepared as dried wet explants byexcising from seed following hydration/imbibition where the explant issubsequently dehydrated and stored, including combinations thereof. Theexplants may be of various ages. In one embodiment, explants arerelatively “young” in that they have been removed from seeds for lessthan a day, for example, from about 1 to 24 hours, such as about 2, 3,5, 7, 10, 12, 15, 20, or 23 hours prior to use. In other embodiments,explants may be stored for longer periods, including days, weeks, monthsor even years, depending upon storage conditions used to maintainexplant viability. Those of skill in the art in particular willunderstand that storage times may be optimized such that the qualityand/or yield of transformants as well as the efficiency of thetransformation process is maximized. This can be carried out for anyparticular transformation protocol, for example, such asAgrobacterium-mediated transformation, microprojectile bombardmenttransformation, as well as other transformation procedures.

Prior to embryo excision, seeds may be subjected to an optional cullingstep intended to remove seeds with a high degree of bacterial or fungalcontamination and also seeds that may for any reason would be unlikelyto produce viable embryonic tissue for use with the present invention.Culling may be carried out, for example, based on parameters such as thesize, color, or density of the seed or other physical characteristicsthat in other contexts would be unobjectionable, and may be adjustedempirically by variation of the excision, sterilization, and storageparameters and by measurement of ultimate yields of viable tissue and ofregeneration and transformation efficiencies. Examples of cullingmethods may include the use of an automatic scale after size sorting. Anoptical sorter suitable for this purpose is the Sortex Seed Sorter orthe Satake ScanMaster™ II (Satake USA Inc., Houston, Tex.). Otherculling techniques may also be employed including culling by moisturecontent.

In certain embodiments of the invention, recovered dry explants may bewashed prior to use in a fluid, which can be a gas or liquid. An exampleof use of a gas includes flushing dry explants in sterile air whilede-ionizing explants to remove static. Further, specifically chargedplates and UV germicidal lamps can be used to remove undesirableparticles such as contaminants and microscopic dust. Dry explants mayalso be subjected to a hydration (pre-culture) to increase internalmoisture content prior to being transformed with a heterologous nucleicacid. Transformation is alternatively carried out prior to priming orgermination. In this embodiment, seed and/or explant sterilization iscarried out, e.g., using Cl gas, followed by chipping or breaching ofthe seed protective outer skin by other means, allowing infiltration ofa liquid Agrobacterium culture. This process can be carried outimmediately following the sterilization and breaching of the seed coat,or after continued storage.

The invention may in particular aspects involve sterilization ofexplants prior to excision and/or post-excision. Sterilization caninclude contacting seed or explant material with various fluids (i.e.liquid or gaseous) that serve to reduce or eliminate the presence ofviable bacterial or fungal contaminants that could otherwise interferewith seed or embryo viability and later plant tissue culture.Sterilization by application of liquid may also hydrate or partiallyhydrate the plant tissues, and serve the purpose of priming seeds orembryos. Methods for sterilization include, but are not limited to, useof chlorine gas, ozone, solutions of bleach or alcohol, ultravioletlight, temperatures of −20° C. or lower, and exposure to a temperaturehigher than 40° C.

Splitting of seeds to isolate the explant may be performed manually orby an individual using a variety of mechanical techniques in order toisolate the explant. Seeds may be split in half along the axis of thecotyledon, using tools such as forceps or by hand. For instance, a seedmay be split or fractured along the axis of the cotyledon by applyingdirect pressure to the seed along the same axis. This may beaccomplished, for example, by striking the seed with a hard object, orby using a press, such as a standard arbor press (e.g. Dayton 4Z328A orDayton 4Z329D; Dayton Tool Company, Dayton, Ohio). Some seeds will splitsuch that the explant may be immediately separated. Other seeds maysplit along the axis of the cotyledon, but may still require additionalmanipulation to isolate the explant. Automated mechanical excision ofhydrated embryo tissue comprising meristems may also be attempted byputting seeds through counter rotating cylinders and collectingresulting seed material, for instance as is described in U.S. PatentPublication 20050005321.

In some embodiments, a dry seed or an explant may be first primed, forexample, by imbibition of a liquid such as water or a sterilizationliquid, redried, and later used for transformation and regeneration. Inother embodiments, the seed or the explant may be primed by raising theinternal seed moisture content to greater than 30%, holding the seed orthe explant at a time point, and then re-initiating imbibition at alater time point. In an alternative embodiment, the seed or the explantmay be primed by raising the internal moisture content to greater than30%, storing the seed or the explant for a predetermined period, dryingthe seed or the explant to the internal moisture content of below 20%,and then re-initiating imbibition.

In another embodiment of the invention, explant quality yield can beoptimized by pre-orientation of seeds prior to seed disassembly. In thismanner, the relatively random impact of the seeds hitting a roller in anautomated machine is controlled, thus controlling the splitting of theseeds between the cotyledon halves.

Any method to separate desired explant material from individual splitseeds or the bulk yield of split seeds may be used (e.g. a process asshown in FIG. 6, or use of an apparatus as shown in FIGS. 2-5 and FIGS.10-11), for instance by automated processing. Such methods may includeaspiration in which a partial vacuum is applied to a first chambercontaining bulk yield from the rice sheller or other machine. The firstchamber consists of a series of alternating angled sides. As seedmaterial falls down these sides and into a collection vessel, ventedslots in the chamber allow lighter material to be pulled into a secondchamber. Airflow, and thus the weight of the seed material being pulledthrough, is controlled by valves. FIG. 6 describes an exemplaryautomated process for excising and separating explant material from seedcoats and other tissues. Following excision the excised explant may thenbe stored under appropriate temperature and moisture conditions forlater use.

In another embodiment of the invention, rather than performing excisionof bulk seed, seeds are singulated prior to explant excision, andexcision is performed on the singulated seed, for instance, via a highthroughput method (e.g. FIGS. 2-5). The seed (e.g. a soybean seed) maybe manipulated by a vacuum cup system to locate the seed, and thenplaced between holders such as a set of vacuum cups or serratedsurfaces. In a particular embodiment the seed coat is removed by use ofa blast of high pressure air or other fluid, or particles, to pulse orblast the seed coat from the seed. The seed tissue may then bemanipulated and placed into a suitable container for furthermanipulation, such as embryo excision, culling, processing, storage, andtransformation. In another embodiment, culling, selection, or otherprocessing steps may occur prior to seed singulation. The singulatedseed may be at a predetermined moisture level, for instance asdetermined by storage conditions following seed harvest. The singulatedseed may be automatically imaged for analysis of pre-determined quality,for instance, to test for viability, chemical and biological properties,and suitability in the transformation or regeneration process. Theexcised explant may be stored under appropriate temperature and moistureconditions for later use. An apparatus for high throughput excision oftransformable meristematic tissue from singulated seed is also anembodiment of the invention (e.g. FIGS. 2-5).

Another method for separating explant material is by manual sieving.Bulk yield from the rice sheller or other machine is put through aseries of geological separation sieves, such that unwanted large andsmall debris are separated from the desired explant by size exclusion.This is effectively accomplished, for instance with soybean material,using U.S. Standard sieves (listed from top to bottom): #7 (2.8 mmopening), #10 (2.0 mm opening), #16 (1.18 mm opening), and then acollection pan on the bottom. Large debris collected on either the #7 or#10 sieves, while desired embryo explant material is retained andcollected on the #16 sieve. Unwanted fine particles passed through tothe collection pan. The explant yield collected on the #16 sieve may befurther purified by placing this yield into a vertical airflowseparation column (e.g. an OREGON SEED BLOWER; Hoffman Manufacturing,Jefferson, Oreg.) in which air is passed through the material, blowinglighter unwanted material upward where it is trapped for removal.Modification of the column with various static reduction means wouldallow for dust removal from embryo surfaces and reduce bio-contaminationand remove any unnecessary plant cell and tissue.

Mechanized sieving and airflow separation may also be utilized. Forinstance, bulk yield from the Rice Sheller is fed into a machine thatutilizes vibration and gravitational pull to sieve and separate theunwanted seed material from the desired explants. As an example, theCLIPPER OFFICE TESTER (Clipper Separation Technologies; A.T. FerrellCompany, Bluffton, Ind.) may be utilized. This machine has two slots forseparation screens to be inserted, whereby seed material is separatedaccording to size. In addition, this machine utilizes a fan thatduplicates the function of the previously mentioned vertical airflowseparation device, thus giving a final purified yield of explants(FIG. 1) in a single step.

In one embodiment, a machine for splitting the seeds is stacked over amechanical separator for continuous flow-through of material and forgreater automation (FIGS. 10-11). The seeds are placed in the machinesuch as a Grainman® Laboratory Paddy Rice Sheller (e.g. Model#64-115-60-WDC; Grain Machinery Manufacturing Corp., Miami, Fla.). Muchof the light material such as seed coats are separated by aspirationduring the excision/splitting process (e.g. FIG. 2, FIG. 6) and theheavier seed fractions i.e., cotyledon pieces and the explants falldirectly into a mechanical separator which separates the cotyledons fromthe explants by way of size exclusion by using vibrating sieves andgravity. Airflow is used to aspirate dust and other light seed debrisout during separation (e.g. FIGS. 7-9).

Regenerable transformable explants may be harvested that contain no,some, or a part of each cotyledon remaining attached to the embryonictissue, for example as much as ¼ of the cotyledon. These explants areconsidered substantially similar, as they may each result in a stabletransformed plant. The explant should however contain at least some ofthe meristematic region of the embryo such that typically the explantcan produce a shoot within 12 weeks of the onset of tissue culturegrowth conditions.

The explant may be recovered from a hydrated seed, from dry storableseed, from a partial hydration of dried hydrated explant, wherein“hydrating” or “hydration” is defined as any act to yield an increase inthe moisture content of a seed and/or explant, without limitation as towhether or whether not the seed and/or explant being hydrated has beensubject to dehydration. An explant may be from seed that is “primed”;that is, a seed that has initiated germination but has beenappropriately placed in stasis pending favorable conditions to completethe germination process. Those of skill in the art will be able to usevarious hydration methods and optimize length of incubation time priorto transformation. The resulting novel explant is storable and cangerminate and or be transformed when appropriate conditions areprovided. Thus the new dry, storable meristem explant may be referred toas an artificial seed.

Examples of such hydration and priming conditions are presented below inTables 4-8. For instance, Table 4 illustrates placing explants followingexcision in a 15 mL conical tube with 5 ml of sterile distilled water(SDW) for a period of 4 hours. A typical protocol for machine excision,such as the “SOP” treatment, may involve placing seeds for 15 minutes ina bleach solution of 200 ppm active Cl, followed by a 2 hour period ofno liquid exposure, followed by an overnight hydration in either beangermination medium (BGM) or a bleach solution of 50 ppm active Cl.

Following excision, one of skill in the art may store the explantaccording to the disclosed methods prior to subsequent use. Methods andparameters for drying, storing, and germinating seed are known in theart (e.g. Senaratna et al., 1983; Vertucci and Roos, 1990; Chai et al.,1998). Storage of excised meristems in accordance with the currentinvention may be carried out using modifications of such storageconditions as desired. Any such conditions may be used as desired,including at temperatures, for example, of from about −80° C. to about60° C. Temperatures of about −20° C. to room temperature in particularhave been found to function well, but the invention is in no way limitedto these temperatures.

The data described in the Examples illustrates, for instance, thatstored seed explants comprising meristematic tissue may remain viableand useful for subsequent genetic transformation and regeneration forweeks or months following excision from seeds (e.g. Example 11 and Table14). Manipulation of excision, sterilization, storage, hydration,rehydration, and transformation parameters allows development ofefficient automated high throughput plant transformation protocols.

A number of parameters for obtaining and handling explants may bevaried. In one embodiment, the excision method may be manual; in analternative embodiment excision occurs by an automated process. In otherembodiments sterilization may be performed by contacting a seed orexplant with a liquid sterilizing agent. In an alternative embodiment, aseed or an explant may be contacted with a gaseous sterilizing agent. Inan alternative embodiment, a seed or an explant may be contacted with anirradiating sterilizing agent such as UV light. FIGS. 7-9 illustrateapparatuses for such sterilization methods. In an alternativeembodiment, a seed or an explant may be sterilized by subjecting theseed or the explant to a brief period of high temperatures so as toreduce the vigor of biological contaminants such as adventitiousbacteria and fungi on the surface of the seed or the explant withoutreducing the vigor of the seed or the explant. This can be achieved at atemperature higher than 40° C.; preferably the temperature is between40° C. to 90° C. The temperature can be raised, for instance, by eitherforced heated air or steam. Such temperatures can be provided by dryersproduced by Bry-Air Inc. (Sunbury, Ohio. USA). In still a furtherembodiment, moisture content of the seed at the time of excision may bevaried. In another embodiment, the temperature of the seed at the timeof excision may be varied. In other embodiments, a storage parameterfollowing excision may be varied. For instance, in one embodiment therelative humidity under which explant storage occurs may be varied. Inanother embodiment, the explant storage temperature may be varied. Inyet other embodiments, the length of explant storage time may vary. Inyet other embodiments, the composition of the medium in which theexplant is stored may vary. Further parameters that may be manipulatedinclude hydration and rehydration media compositions, incubationtemperature, length of time, and transformation methods, among others.

Various methods have been developed for transferring genes into planttissue including high velocity microprojection, microinjection,electroporation, direct DNA uptake and, bacterially-mediatedtransformation. Bacteria known to mediate plant cell transformationinclude a number of species of the Rhizobiaceae, including, but notlimited to, Agrobacterium sp., Sinorhizobium sp., Mesorhizobium sp., andBradyrhizobium sp. (e.g. Broothaerts et al., 2005: U.S. PatentApplication Publication 20070271627). Targets for such transformationhave often been undifferentiated callus tissues, although differentiatedtissue also has been used for transient and stable plant transformation.

Bacterially-mediated gene delivery (e.g. Agrobacterium-mediated; U.S.Pat. No. 5,563,055; 5,591,616; 5,693,512; 5,824,877; 5,981,840) can bemade into cells in the living meristem of an embryo excised from a seed,such as soybean (e.g. U.S. Pat. No. 6,384,301). The meristematic regionmay be cultured in the presence of a selection agent such as theherbicide glyphosate. The result of this step is the termination or atleast growth retardation of most of the cells into which the foreigngenetic construction has not been delivered and the simultaneousinduction of the formation of shoots, which arise from a small clusterof cells including a transformed meristematic cell. The meristem canalso be cultivated in the presence of other selection agent alone or incombination, including, but not limited to auxin-like herbicides such asdicamba or 2,4-D, MCPA, glufosinate, acetolactate synthase inhibitors,protoporphyrinogen oxidase inhibitors, andhydroxyphenyl-pyruvate-dioxygenase inhibitors, neomycin, kanamycin,paramomycin, G418, aminoglycosides, spectinomycin, streptomycin,hygromycin B, bleomycin, phleomycin, sulfonamides, streptothricin,chloramphenicol, methotrexate, 2-deoxyglucose, betaine aldehyde,S-aminoethyl L-cysteine, 4-methyltryptophan, D-xylose, D-mannose,benzyladenine-N-3-glucuronidase. Examples of various selectable markersand genes providing resistance against them are disclosed in Miki andMcHugh, 2004. In one embodiment of the invention a coding region for theselectable marker aminoglycoside adenyltransferase (aadA) conferringresistance to spectinomycin or streptomycin is used (e.g. U.S. Pat. No.5,217,902; or Sandvang, 1999).

As is well known in the art, other methods for plant transformation maybe utilized, for instance as described by Miki et al, (1993), includinguse of microprojectile bombardment (e.g. U.S. Pat. No. 5,914,451; McCabeet al., 1991; U.S. Pat. Nos. 5.015,580; 5,550,318; 5,538,880).

Unmodified and modified protein molecules and their correspondingnucleic acid molecules providing herbicide tolerances to one or more ofthese herbicides are well known in the art. They are exemplified belowand are incorporated herein by reference:

a) sequences encoding tolerance to glyphosate include5-enolpyruvylshikimate-3-phosphate synthases (EPSPS; U.S. Pat. No.5,627,061, U.S. Pat. RE39,247, U.S. Pat. Nos. 6,040,497, 5,094,945,WO04074443, and WO04009761), glyphosate oxidoreductase (GOX; U.S. Pat.No. 5,463,175), glyphosate decarboxylase (WO05003362 and U.S. PatentApplication 20040177399), and glyphosate-N-acetyl transferase (GAT: U.S.Patent publication 20030083480) conferring tolerance to glyphosate;

b) dicamba monooxygenase (DMO, encoded by ddmC) conferring tolerance toauxin-like herbicides such as dicamba (U.S. Patent Applications20030115626, 20030135879; Wang et al., 1996; Herman et al., 2005);

c) phosphinothricin acetyltransferase (bar) conferring tolerance tophosphinothricin or glufosinate (U.S. Pat. Nos. 5,646,024, 5,561,236, EP275,957; U.S. Pat. Nos. 5,276,268; 5,637,489; 5,273,894);

d) 2,2-dichloropropionic acid dehalogenase conferring tolerance to2,2-dichloropropionic acid (Dalapon) (WO9927116);

e) acetohydroxyacid synthase or acetolactate synthase conferringtolerance to acetolactate synthase inhibitors such as sulfonylurea,imidazolinone, triazolopyrimidine, pyrimidyloxybenzoates and phthalide(U.S. Pat. Nos. 6,225,105; 5,767,366, 4,761,373; 5,633,437; 6,613,963;5,013,659; 5,141,870; 5,378,824; 5,605,011):

f) haloarylnitrilase (Bxn) for conferring tolerance to bromoxynil(WO8704181A1; U.S. Pat. No. 4,810,648; WO8900193A);

g) modified acetyl-coenzyme A carboxylase for conferring tolerance tocyclohexanedione (sethoxydim) and aryloxyphenoxypropionate (haloxyfop)(U.S. Pat. No. 6,414,222);

h) dihydropteroate synthase (sulI) for conferring tolerance tosulfonamide herbicides (U.S. Pat. Nos. 5,597,717; 5,633,444; 5,719,046);

i) 32 kD photosystem II polypeptide (psbA) for conferring tolerance totriazine herbicides (Hirschberg et al., 1983);

j) anthranilate synthase for conferring tolerance to 5-methyltryptophan(U.S. Pat. No. 4,581,847);

k) dihydrodipicolinic acid synthase (dapA) for conferring to toleranceto aminoethyl cysteine (WO8911789):

l) phytoene desaturase (crtI) for conferring tolerance to pyridazinoneherbicides such as norflurazon (JP06343473);

m) hydroxy-phenyl pyruvate dioxygenase for conferring tolerance tocyclopropylisoxazole herbicides such as isoxaflutole (WO 9638567; U.S.Pat. No. 6,268,549);

n) modified protoporphyrinogen oxidase I (protox) for conferringtolerance to protoporphyrinogen oxidase inhibitors (U.S. Pat. No.5,939,602); and

o) aryloxyalkanoate dioxygenase (AAD-1) for conferring tolerance to anherbicide containing an aryloxyalkanoate moiety (WO05107437). Examplesof such herbicides include phenoxy auxins (such as 2,4-D anddichlorprop), pyridyloxy auxins (such as fluroxypyr and triclopyr),aryloxyphenoxypropionates (AOPP) acetyl-coenzyme A carboxylase (ACCase)inhibitors (such as haloxyfop, quizalofop, and diclofop), and5-substituted phenoxyacetate protoporphyrinogen oxidase IX inhibitors(such as pyraflufen and flumiclorac).

A variety of tissue culture media are known that, when supplementedappropriately, support plant tissue growth and development, includingformation of mature plants from excised meristems or embryos. Thesetissue culture media can either be purchased as a commercial preparationor custom prepared and modified by those of skill in the art. Examplesof such media include, but are not limited to those described byMurashige and Skoog, (1962); Chu et al., (1975); Linsmaier and Skoog,(1965): Uchimiya and Murashige, (1962); Gamborg et al., (1968); Duncanet al., (1985); McCown and Lloyd, (1981); Nitsch and Nitsch, (1969); andSchenk and Hildebrandt, (1972), or derivations of these mediasupplemented accordingly. Those of skill in the art are aware that mediaand media supplements such as nutrients and growth regulators for use intransformation and regeneration are usually optimized for the particulartarget crop or variety of interest. Reagents are commercially availableand can be purchased from a number of suppliers (see, for example SigmaChemical Co., St. Louis, Mo. and Phytotechnology Laboratories, ShawneeMission, Kans.).

Co-culture and subsequent steps may be performed in dark conditions, orin lighted Percival incubators, for instance for 2 to 5 days with aphotoperiod of 16 hours of light, 8 hours of dark. In one embodiment,the light intensity may be, for example, at least about 5 E, including,at least about 10 μE or 25 μE, including between about 5 uE and about200 uE or other lighting conditions that allow for normal plastiddevelopment at a temperature of approximately 23 to 25° C., and may beperformed at up to about 35° C.

EXAMPLES

Those of skill in the art will appreciate the many advantages of themethods and compositions provided by the present invention. Thefollowing examples are included to demonstrate the preferred embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the examples that follow representtechniques discovered by the inventors to function well in the practiceof the invention, and thus can be considered to constitute preferredmodes for its practice. However, those of skill in the art should, inlight of the present disclosure, appreciate that many changes can bemade in the specific embodiments that are disclosed and still obtain alike or similar result without departing from the spirit and scope ofthe invention. All references cited herein are incorporated herein byreference to the extent that they supplement, explain, provide abackground for, or teach methodology, techniques, or compositionsemployed herein.

Example 1 Separation of Explant Material

Seeds were processed manually, or subjected to automated excision in arice sheller (e.g. Grainman® Laboratory Paddy Rice Sheller (e.g. Model#64-115-60-WDC; Grain Machinery Manufacturing Corp., Miami, Fla.), orfor instance as described in U.S. Patent Publication 20050005321. Inorder to obtain meristematic explant material, soybean seeds (cv. A3525;Asgrow Seed Company) were processed to separate the embryo, comprisingmeristematic tissues, from the seed coat and cotyledon(s). The effect ofthe internal moisture content of the starting seed at the time ofexcision on explant yield from this process is shown in Table 1.

TABLE 1 Effect of Internal Moisture Content on Explant Yield MoistureContent Explant estimate per of Soybean Seed Kg of seed processed 6.3%1626 8.2% 939 11.5% 87

The temperature of the seed prior to preparation of explant materialalso affected explant yield. Table 2 illustrates that explants can beexcised at various temperatures, including −20° C. to room temperature.

TABLE 2 Effect of Seed Storage Temperature on Explant Yield Meristemestimate per Storage temperature Kg of seed processed Room temperature650.4 (about 23-26° C.)  4° C. 286.2 −20° C. 267.3

Example 2 Recovery of Explant Material

Table 3 illustrates the yield of usable explant tissue given differingseed moisture content at the start of the excision procedure. Lower seedmoisture (about 6.2%) allowed for greater yield of explant material byweight of seed processed. This is noteworthy, as the internal moisturecontent of dry soybean seed when freshly harvested from the field isapproximately 9 to 14% and is ideally maintained at about 11% for longterm (1 to 20 years) storage. The higher moisture content allows theseeds to be handled without breakage and loss of vigor to the embryo.The inventors discovered that dry seed at the higher moisture contentwere much less brittle than seed dried to lower internal moisturecontents (3% to 7%). This discovery allows seed to be handled and storedat the ideal internal moisture content for vigor (approximately 9 to12%), yet manipulated for ideal extraction of dry explants (artificialseeds) by drying seeds to approximately 3% to 7% to achieve abrittleness. This brittle state maintains vigor of the embryo, yetallows for a clean split of the seed between the cotyledons, and thusallows both high quality, and high yield.

The optimum moisture content to achieve a brittle state and thus allowhigh process yield and high transformation quality explant may varybased on soybean genotype and crop type. This example illustrates themethodology necessary to optimize conditions for a given germplasmsource or type of plant seeds.

TABLE 3 Yield of usable explant tissue obtained from seeds withdifferent moisture content. Meristem containing Seed Returned Totalexplants by Damaged moisture embryo sample microscopic explants contentRun size yield % Crude weight evaluation or debris (%) (grams) (grams)yield (mg) (mg) (mg) 12.5 4203 67.6 1.6 500 170 328 12.2 200 3.98 2.0500 160 340 12.2 200 3.71 1.9 500 225 275 14.5 200 3.25 1.6 500 320 18014.5 200 3.28 1.6 500 250 250 6.2 200 6.35 3.2 500 200 300 6.2 200 6.083.0 500 230 270 Number Meristem % Seed of good estimate Meristem Seedrecovery moisture % good explants for total estimate estimate based oncontent explants per 1000 mg run per kg per kg theoretical (%) by weightsample (count) (count) (count) maximum 12.5 34 68 4597 1094 6050 18.112.2 32 64 255 1274 6050 21.1 12.2 45 90 334 1670 6050 27.6 14.5 64 126410 2048 6050 33.8 14.5 50 102 335 1673 6050 27.6 6.2 40 80 508 25406050 42.0 6.2 46 96 584 2918 6050 48.2

Example 3 Sterilization of Seeds and/or Explant Material

A number of techniques of sterilizing seeds before excision, as well assterilizing explants after excision from the seeds were tested.Post-excision sterilization of dry explants using chlorine gas in avacuum desiccation chamber was tested at time intervals ranging from 15minutes to 16 hours. Contamination control increased with longerexposure to Cl gas, although fungal contamination grew in treatments inwhich the exposure to Cl gas had surpassed the survivable threshold ofthe explants.

Ozone gas treatments were also tested. Both whole seed (before excision)and dry explants (after excision) were exposed to O₃ gas in a PLEXIGLASchamber (OSR-8 Ozone Generator; Ozone Solutions. Sioux Center, Iowa) atvarious time intervals of 1-24 hours. O₃ was used at a concentration of467 ppm. After seed was exposed to ozone, embryonic material was excisedand explant viability was measured. Ozonation of soybean seed for 12hours or less did not impact viability of subsequently isolatedexplants, but drastically decreased bioburden found in explants.Ozonation of dry excised explants for as little as 1-4 hours decreasedexplant health (i.e. number of viable embryos).

Additional tests on pre-excision sterilization of whole seed wereperformed using a bleach solution of 200 ppm active chlorine, followedby an overnight hydration period (˜9 hours) in a solution of 50 ppmactive chlorine. These seeds were then allowed to dry in a laminar flowhood (typically for 12-48 hours) before being excised mechanically. Amodification to the 50% bleach soak protocol was also tested, in whichthe seeds were first rinsed with a 70% solution of ethanol. The ethanolwas immediately drained (total exposure to ethanol was less than 5seconds), and then the 50% bleach soak was performed by treating seeds3-15 min in 50% bleach followed by 3 rinses with water and drying theseeds overnight such that the moisture content was less than 8%. UVlight may also be employed to sterilize the plant material.

Example 4 Hydration of Seeds and Explant Material

Studies employing new pre-culture hydration/germination strategies weretested. The types of media used for this step included “bean germinationmedium” (BGM; Media Table 11), soy inoculum medium (INO; Media Table11), and prepared log-phase Agrobacterium growth cultures (AGRO). TheAgrobacterium growth culture was grown overnight in Lysogeny Broth (LB,also commonly referred to as Luria-Bertani Broth) to log phase, and thencentrifuged and resuspended to a final optical density at 660 nm of 0.25to 0.6. The medium used for the dilution is the same as the soy inoculummedium. Plant Preservative Mixture (PPM™. Product #P820; PhytotechnologyLaboratories, Shawnee Mission, Kans.) was also tested at a concentrationof 2 mg/L (as per manufacturer recommendations on label). Explants weresoaked in this solution overnight at 4° C. Other variations were made inthe duration of exposure to respective hydration media, the varioustemperatures during this exposure, and the extent of saturation in therespective media. Exposure times tested ranged from 0 to 24 hours.Temperatures during longer exposure times (those greater than 4 hours)were either room temp (˜26° C.), 23° C., or 4° C. Exposure times of 4hours or less were all tested at room temperature. As an alternative tocompletely submerging or substantially saturating explants with liquidmedia during the hydration process, some treatments employed the use ofmoistened filter paper (enough liquid to wet, but not to saturate). Thiswas done with filter paper moistened with either BGM orAgrobacterium-culture medium. Hydration was performed in a variety ofvessels, including but not limited to conical centrifuge tubes,graduated glass bottles, or a PLANTCON tissue culture container (MPBiomedicals, Irvine, Calif.).

This example also demonstrates that hydration can be done in a varietyof media containing various types of carbohydrates such as glucose(INO), and sucrose (BGM). Other carbohydrates such as galactose may beuseful in hydration medium.

Example 5 Transformation and Cultivation of Soybean Explants

Agrobacterium-mediated transformation followed the hydration step asindicated in Tables 4-9. Soybean meristem explants were transformed withpMON67438 comprising a CP4 EPSPS gene conferring glyphosate toleranceand a GUS reporter gene. Explants that had been hydrated in somethingother than Agrobacterium culture medium, i.e. soy inoculum medium (INO)or sterile distilled water (SDW), bean germination medium (BGM), orPlant Preservative Mixture, had that liquid removed, and then theexplants were rinsed twice with sterile distilled water. Explants werethen placed in a PLANTCON (if not already in one). PreparedAgrobacterium culture (as described above) was added to the container(enough to cover all explants within the PLANTCON). Explants that werehydrated in Agrobacterium culture to begin with remained in thatculture, and were also transferred to a PLANTCON. Explants were thensubjected to sonication wounding for 20 seconds while in the PLANTCONaccording to standard procedures (U.S. Pat. No. 7,002,058). Followingsonication wounding, explants were transferred to new PLANTCONScontaining a cut-to-size piece of filter paper. 2.5 mL to 5 mL of soyinoculum medium was used to moisten the filter paper. Explants wereco-cultured at 23° C. for 2-4 days either in dark or light. Followingco-culture, explants were placed on the surface of solid woody plantmedium (WPM; Table 12), and implanted into solid woody plant medium atapproximately the 17^(th) day post-inoculation, for the remainder of thetissue culture experiment phase. Shoots were transferred to Bean RootingMedium for rooting (BRM: Table 13). Concentrations of various hormonesmay be manipulated to effect regeneration. For examples, BAP may be usedat 0.04 ppm (0.18 μM) in WPM and IAA may be used at about 0.099 ppm(0.565 μM) in BRM. Other plant growth regulators and concentrations havebeen routinely utilized to facilitate transformation and regeneration,for instance as described in U.S. Pat. No. 6,384,301.

Explants that had been placed within assay well plates for initialhydration were left there for the entire duration of the experiment lifespan, including sonication and co-culture periods. For theseexperiments, liquid media was used instead of solid media, and wasreplaced with fresh media at ˜17 days post inoculation. Thisdemonstrates that the explants are amenable to liquid culture as well assolid (gel-based) tissue culture steps.

Example 6 Comparison of Explant Excision, Sterilization, Storage, andHydration Parameters

Subsequent studies tested a variety of parameters involving seedstorage, excision, and sterilization methods and conditions; explantstorage conditions: and transformation conditions as they impacted theability of excised meristematic material to initiate shoot formation(SF), whether or not having been transformed, as well as transformationfrequency (TF). These parameters, for either or both seed and explantmaterial, included pre- or post-excision sterilization procedures,storage conditions, hydration conditions, and subsequent tissue cultureconditions, including in the absence or presence of selection.

In study SAG_709 (Table 4), whole soybean seed were sterilized prior toexcision by immersion in a 50% sodium hypochlorite (bleach) solution.Following sterilization, seeds were rinsed and dried to a moisturecontent of <8%. Following these steps, explants were prepared andrecovered as described in examples 1 and 2. Parameters studied included:length of storage prior to transformation of explant material: storagetemperature; and hydration media. The results showed that the explantsof the present invention can be used to obtain transformed plants undera broad range of storage temperature and a variety of hydration media.The result of DNA testing showed a normal distribution for copy numbersbased on the sample size.

In Study SAG_712 (Table 5), soybean seeds were sterilized with Cl gasprior to dry excision. Following sterilization and dry excision, lengthof storage and hydration conditions were varied. This was compared withwet excision method as described in U.S. Publ. 20050005321 and U.S. Pat.No. 7,002,058 (Trt 7).

In Study SAG_714 (Table 6), seeds were sterilized prior to excision byimmersion in a 50% sodium hypochlorite (bleach) solution. Followingsterilization, rinsing, drying, and dry excision, explants were storedfor one to three days prior to transformation at various temperatures(e.g. −20° C., 4° C., and room temperature), and hydration conditionswere also varied. The ability of explants treated in this manner to formshoots (shoot frequency; “SF”) or transformed plants (transformationfrequency; “TF”) was compared with explants that were prepared by a “wetexcision” method, for instance as described in U.S. Patent ApplicationPublication 20050005321 and then dried and stored (Trt 7 and Trt 8).

Transformation has also been demonstrated in explants that wererecovered from a hydrated or imbibed seed (referred to as “wet excision”in study SAG_714—Table 6, treatments 7 and 8; and also in studySAG_762—Table 8, treatments 1 and 2) but where the explant wasappropriately dehydrated. Wet excision methods are described in U.S.Publ. 20050005321 and U.S. Pat. No. 7,002,058. A typical process forpreparing explants by this method is as follows:

1) Dry seeds are rinsed with sterile water, or a solution of Sodiumhypochlorite (ranging from 0 ppm to ˜30,000 ppm active chlorine,including 50 ppm and 200 ppm active chlorine) for 3 to 20 minutes.Liquid is then drained.

2) Approximately 2 hours later, rehydration medium is applied for 5 to24 hours. This rehydration medium can be BGM, sterile deionized water,sterile or clean tap water, or a dilute disinfectant solution, such assodium hypochlorite with an active chlorine content of 50 to 1000 ppm.

3) Following rehydration medium, the seeds may be immediately excised toisolate embryo explants (either by mechanical or manual methods), or maybe further rinsed with water or other dilute disinfectant, such assodium hypochlorite with an active chlorine content of 50 to 1000 ppmfor 15 minutes.

4) Following its excision and recovery, the explant is dried andprepared for storage by being spread out in a shallow tray under a flowof air. This is typically done in a clean-air tissue culture hood.Explants were typically allowed to dry for ˜18 to 24 hours.

5) Dried explants were stored (typically in sealed 50 mL conical tubes).Storage duration prior to transformation initiation can range fromminutes to weeks or months. Temperature conditions during storage canrange from room temperature to ⁻80 degrees C.

6) Following desired storage, explants were hydrated for transformationas described in example 4.

Study 716 (Table 7) tested the effect of a 7 day storage periodfollowing dry excision on the ability of explants to form shoots.

Study 762 (Table 8) tested the effect of a 7 week storage period on theability of excised explant material to form shoots. A dry excised embryothat was stored for up to 7 weeks was able to produce a transgenicplant.

An overall summary of shoot-formation and transformation frequencies forthe above listed studies is found in Table 9. The results indicate thatdry excised as well as wet-excised (and then dried) soybean explantsremain viable, retain the ability to form shoots and plants, and may besuccessfully transformed with heterologous DNA, even after dry storageof excised embryos for periods of time up to 8 weeks under a variety oftemperature conditions and types of hydration media. Shoot formationfrequency (SF) and transformation frequency (TF) of dry excised andstored explants or wet excised, dried, and stored explants comparedfavorably with those of explants that were not stored, according topreviously described methods (U.S. Publ. 20050005321). The copy numberand presence of introduced transgenes (e.g. CP4), and presence of vectorbackbone sequences (e.g. oriV) was also tested by Southern analysis orby INVADER assay (e.g. Mein et al., 2001) at the R0 generation (Tables5-9). DNA analysis of R1 plants yielded the same results demonstratingstable and heritable transformation

TABLE 4 SAG709 Trt 1 Trt 2 Trt 3 Trt 4 Trt 5 Trt 6 SterilizationPre-excision sterilization in 50% bleach conditions Storage 2 days @ 2days @ 2 days @ 2 days @ 2 days @ 1 day @ conditions Room Temp Room TempRoom Temp 4° C. 4° C. 4° C. Hydration 4 hours 4 hours 4 hours 4 hours 4hours 4 hours conditions in 15 mL in 15 mL in 15 mL in 15 mL in 15 mL in15 mL conical conical conical conical conical conical tubes; tubes;tubes; tubes; tubes; tubes; 5 mLs INO 5 mLs agro 5 mLs SDW 5 mLs INO 5mLs agro 5 mLs SDW Explants used 35 34 39 36 56 53 Shoots 3 0 7 7 13 5obtained SF 8.57% 0.00% 17.95% 13.44% 23.21% 9.43% Rooted shoots 1 0 0 32 1 obtained GUS positive 1 0 0 3 2 1 root assay TF 2.86% n/a n/a 9.33%3.57% 1.89% DNA test Results for copy number (OriV − or +) Negative 0 00 0 1 Copy 0 0 0 2 (−) 2 Copy 0 0 0 1 (−) 1 3 Copy 0 0 0 0 >/= 4 Copy 1(−) 0 0 0 1 (+) 1 (−) Trt 7 Trt 8 Trt 9 Trt 10 Trt 11 SterilizationPre-excision sterilization in 50% bleach conditions Storage 1 day @ 1day @ 2 days @ 2 day @ 2 day @ conditions 4° C. 4° C. −20° C. −20° C.−20° C. Hydration 4 hours 4 hours 4 hours 4 hours 4 hours conditions in15 mL in 15 mL in 15 mL in 15 mL in 15 mL conical conical conicalconical conical tubes; tubes; tubes; tubes; tubes; 5 mLs INO 5 mLs agro5 mLs INO 5 mLs agro 5 mLs SDW Explants used 52 96 42 39 30 Shoots 10 99 6 4 obtained SF 19.23% 9.38% 21.43% 15.38% 13.33% Rooted shoots 1 2 32 1 obtained GUS positive 1 1 3 1 1 root assay TF 1.92% 2.08% 7.14%5.13% 3.33% DNA test Results for copy number (OriV − or +) Negative NA 1Copy NA 1 (−) 1 (−) 2 Copy NA 1 (−) 1 (−) 3 Copy NA 1 2 1 (−) >/= 4 CopyNA Treatment Averages Average DMA Test (GAMA) Results Treatment SF TFNegative 1-2 copy 3-4 copy >4 copy Room 8.84% 0.95% 0 0 0 100% Temperature 4 degrees 16.14% 3.56% 0 69% 13% 18% −20 degrees 16.72%5.20% 0 33% 67% 0 2 day storage 14.92% 3.80% 0 56% 44% 0 1 day storage12.68% 1.96% 0 67% 33% 0 hydration in Agro 11.99% 2.70% 0 40% 20% 40%hydration in INO 17.17% 5.06% 0 57% 29% 14.0%  hydration in SDW 13.57%1.74% 0 0 100%  0

TABLE 5 SAG_712 Trt 1 Trt 2 Trt 3 Trt 4 Trt 5 Trt 6 Trt 7 SterilizationPre-excision sterilization in Cl gas conditions Storage 2 days @ 2 days@ 2 days @ 1 day @ 1 day @ 1 day @ Conventional conditions 4° C. 4° C.4° C. 4° C. 4° C. 4° C. (e.g., US 2003/0110532) Hydration 4 hours 4hours 4 hours 4 hours 4 hours 4 hours Conventional conditions in 15 mLin 15 mL in 15 mL in 15 mL in 15 mL in 15 mL (e.g.,US conical conicalconical conical conical conical 2003/0110532) tubes; tubes; tubes;tubes; tubes; tubes; 5 mLs INO 5 mLs agro 5 mLs SDW 5 mLs INO 5 mLs Agro5 mLs SDW # of 54 58 47 92 90 91 100 explants/study Number of 3 4 1 16 89 8 shoots obtained SF 5.56% 6.90% 2.13% 17.39% 8.89% 9.89% 8.00% Numberof 0 0 3 2 3 3 rooted shoots obtained GUS positive 3 2 2 3 root assay TFn/a n/a n/a 3.26% 2.22% 3.30% 3.00% DNA test Results for copy number(OriV − or +) Negative 0 0 0 0 0 1 Copy 0 0 0 1 (−) 2 (−) 2 (−) 1 (−) 2Copy 0 0 0 1 (−) 0 3 Copy 0 0 0 0 1 (−) 1 >/= 4 Copy 0 0 0 0 0 TreatmentAverages Average DNA Test (GAMA) Results Treatments SF TF Negative 1-2copy 3-4 copy >4 copy 4 degrees 8.46% 1.46% 0 83% 17% 0% 2 day storage4.86% n/a 0 0 0 0 1 day storage 12.06% 2.93% 0 83% 17% 0 hydration inAgro 7.89% 1.11% 0 100%  0 0 hydration in INO 11.47% 1.63% 0 100%  0 0hydration in SDW 6.01% 1.65% 0 67% 33% 0

TABLE 9 Summary of shoot-formation and transformation frequenciesobtained. Treatment Averages Average DNA Test (GAMA) Results TreatmentsSF TF Negative 1-2 copy 3-4 copy >4 copy Room Temp 9.26% 1.28% 0.00%0.00% 0.00% 100.00% 4 degrees 11.56% 2.46% 0.00% 67.33% 26.67% 6.00% −20degrees 16.72% 5.20% 0.00% 57.00% 42.00% 0.00% 1 day storage 11.86%2.57% 0.00% 83.33% 16.67% 0.00% 2 day storage 9.89% 1.90% 0.00% 56.00%44.00% 0.00% 3 day storage 9.44% 1.80% 0.00% 33.00% 67.00% 0.00% Morethan 7 wk 1.51% 0.08% 0.00% 100.00 0.00% 0.00% storage hydration in INO9.41% 2.18% 0.00% 78.50% 14.50% 7.00% hydration in Agro 8.73% 1.57%0.00% 69.00% 15.67% 4.67% hydration in SDW 7.61% 1.35% 0.00% 55.67%44.33% 0.00% Wet excised & 10.84% 2.04% 0.00% 100.00% 0.00% 0.00% driedDry excised 9.64% 2.03% 0.00% 59.69% 25.58% 14.71%

TABLE 7 SAG_716 Trt 1 Trt 2 Trt 3 Storage 7 days 7 days 7 daysconditions: @ 4° C. @ 4° C. @ 4° C. Hydration 4 hours 4 hours 4 hoursconditions in 50 mL in 50 mL in 50 mL conical conical conical tubes;tubes; tubes; 5 mLs Agro 5 mLs INO 5 mLs SDW Sterilization Pre-excision50% bleach method # of 104 122 96 explants/study Number of 3 1 2 shootsSF 2.88% 0.82% 2.08% Number of 0 0 0 rooted shoots TREATMENT AVERAGES:SF Hydration in Agro 2.88% Hydration in INO 0.82% Hydration SDW 2.08%Avg. all trts at 7 1.93% day storage

TABLE 8 SAG_762 Trt 1 Trt 2 Trt 3 Trt 4 Storage Wet auto Wet auto DryDry conditions: excision, excision, excised, excised, then dried; thendried; stored ~8 stored ~7 stored ~7 stored ~7 wks wks wks wks @ 4° C. @4° C. @ 4° C. @ −20° C. Hydration 4 hours 4 hours 4 hours 4 hoursconditions in 150 mL in 150 mL in 50 mL in 50 mL pyrex pyrex conicalconical beaker; beaker; tubes; tubes; 50 mLs INO 50 mLs INO 25 mLs INO25 mLs INO Sterilization Pre-germination Pre-excision method as per SOP50% bleach # of 425 650 275 321 explants/study Number of 2 12 6 5 shootsSF 0.47% 1.85% 2.18% 1.56% Number of 0 0 0 1 rooted shoots GUS rootassay 1 TF n/a n/a n/a 0.31%

TABLE 6 SAG_714 Trt 1 Trt 2 Trt 3 Trt 4 Trt 5 Trt 6 Trt 7 Trt 8 Storage3 days @ 3 days @ 3 days @ 1 day @ 1 day @ 2 days @ Wet auto Wet autoconditions 4° C. 4° C. 4° C. RT 4° C. −20° C. excision, excision, thendried; then dried; store 1 day store 1 day @ −20° C. @ 4° C. Hydration 4hours 4 hours 4 hours 4 hours 4 hours 4 hours 4 hours in 4 hours inconditions in 15 mL in 15 mL in 15 mL in 15 mL in 15 mL in 50 mL 50 mLtube; 50 mL tube; conical conical conical conical conical conical 5 mLsAgro 5 mLs Agro tubes; 5 mLs tubes; 5 mLs tubes; 5 mLs tubes; 5 mLstubes; 5 mLs tube; 5 mLs INO agro SDW Agro SDW Agro SterilizationPre-excision 50% bleach Post- Standard Standard method excision protocolProtocol Cl gas # of 98 89 72 62 50 86 34 44 explants/study Number of 813 4 6 6 0 7 9 shoots obtained SF 8.16% 14.61% 5.56% 9.68% 12.00% 0.00%20.59% 20.45% Number of 2 3 0 1 2 0 2 1 rooted shoots obtained GUSPositive 2 2 1 2 2 1 Root assay TF 2.04% 3.37% n/a 1.61% 4.00% n/a 5.88%2.27% DNA test Results for copy number (OriV − or +) Negative 1 Copy 1 2Copy 1 2 1 3 Copy 1 1 >/= 4 Copy Treatment Averages Average DNA Test(GAMA) Results Treatments SF TF Negative 1-2 copy 3-4 copy >4 copy 4degrees 10.08% 2.35% 0 50% 50% 0 Room Temp 9.68% 1.61% 0 0 0 0 1 daystorage 10.84% 2.81% 0 100%  0 0 3 day storage 9.44% 1.80% 0 33% 67% 0hydration in Agro 12.14% 2.49% 0 67% 33% 0 hydration in INO 8.16% 2.04%0 50% 50% 0 hydration in SDW 8.78% 2.00% 0 100%  0 0 Wet excised, 20.52%4.08% 0 100%  0 0 then dried

Another parameter that was varied in Agrobacterium-mediatedtransformation was a change in the timing of Agrobacterium cultureonset, and sonication wounding initiation. Instead of waiting for 1 houror more for dry explants to hydrate, sonication wounding procedures insome studies were initiated immediately upon submersion in the hydrationmedium. Alternatively, some treatments received a 1 to 2 day delay inthe onset of Agrobacterium culture inoculation. Instead of beinginoculated immediately after the hydration step, these explants wereplaced on moistened filter paper for the delay period, and theninoculated and sonication procedures were completed. In a differenttreatment, the sonication wounding step was left from the procedurecompletely, as explants were being hydrated on filter paper moistenedwith Agrobacterium culture.

Also tested was a delayed onset of selection pressure (e.g. exposure toglyphosate). Instead of transferring explants onto solid media withselection compound at 2-4 days post inoculation studies received liquidWPM without glyphosate for additional 48 hours, or 1 week before beingtransferred to the solid WPM with selection compound to terminate or atleast retard the growth of non-transformed cells.

An alternative to Agrobacterium-mediated transformation was also tested.Dry excised explants were inoculated with Rhizobium leguminosarumstrains RL 2370LBA & RL 2048G, pMON96033. The protocol forRhizobium-mediated transformation was similar to Agrobacterium-mediatedtransformation, except for replacing the bacterial strain withRhizobium.

A cytokinin, 6-Benzylamino purine (BAP) was also tested as an additiveto the Agrobacterium culture inoculum medium (also referred to as soyinoculum medium, INO) (e.g. McCabe and Martinell, 1993).

Example 7 Preparation and Transformation of Cotton Explants

Excised cotton (cv STN 474) meristem explants dried after excision andstored dried for 30 days or more are viable after re-hydration andco-culture transformation with Agrobacterium. The protocol for cottonmeristem transformation essentially followed the method of McCabe andMartinell (1993). Seeds were excised and prepared as per McCabe &Martinell (1993), with the exception that excised embryos were spreadout and left in an open container until dry. Storage conditions, andseed pre-sterilization, re-hydration, Agrobacterium inoculation,co-culture and tissue culture procedures were essentially identical tothose described for soy. Consistent with results from soybean, shootsand young leaves were observed on cultured cotton explants followingtransformation of meristematic tissue with exogenous DNA.

Example 8 Media Used

TABLE 10 BEAN GERMINATION MEDIA (BGM) COMPOUND: QUANTITY PER LITER BTSTOCK #1 10 mL BT STOCK #2 10 mL BT STOCK #3 3 mL BT STOCK #4 3 mL BTSTOCK #5 1 mL SUCROSE 25 g Adjust to pH 5.8. ADDITIONS PRIOR TO USE: PER1 L CEFOTAXIME (50 mg/mL) 2.5 mL FUNGICIDE STOCK 3 mL BT Stock for BeanGermination Medium Bt Stock 1 (1 liter) KNO₃ 50.5 g NH₄ NO₃ 24.0 gMgSO₄*7H₂O 49.3 g KH₂PO₄ 2.7 g Bt Stock 2 (1 liter) CaCl₂*2H₂O 17.6 g BtStock 3 (1 liter) H₃BO₃ 0.62 g MnSO₄H₂O 1.69 g ZnSO₄7H₂O 0.86 g KI 0.083g NaMoO₄*2H₂O 0.072 g CuSO₄*5H₂O 0.25 mL of 1.0 mg/mL stock CoCl₄*6H₂O0.25 mL of 1.0 mg/mL stock Bt Stock 4 (1 liter) Na₂EDTA 1.116 gFeSO₄*7H2O 0.834 g Bt Stock 5 (500 mL) Thiamine-HC1 0.67 g Nicotine Acid0.25 g Pyridoxine-HC1 0.41 g Fungicide Stock (100 mL) Chlorothalonil(Bravo) 75% WP 1.0 g Captan 50% WP 1.0 g Add sterile distilled water to100 mL

TABLE 11 SOY INOCULUM MEDIUM (INO) amount per liter Stock #1 (Majors) 1mL B5 Stock #2 (Calcium Chloride) 1 mL B5 Stock #3 (Minors) 1 mL B5Stock #5 (Iron) 1 mL Potassium Nitrate (KNO₃) 1 g Glucose 30 g MES 3.9 gAdd water to 1 L Initial pH: Adjusted to 5.4 with KOH Autoclave B5 Stock#4 (Vitamins) (F.S.) 1 mL Store at Room temp. B5 STOCK #1 Amount perliter: TC Water 750 mL Magnesium Sulfate 100 g Ammonium Sulfate 53.6 gSodium Phosphate Monobasic Anhydrous 60 g Stir until completelydissolved Bring to 1 L with TC water B5 STOCK #2 TC Water 750 mL CalciumChloride 60 g Stir until completely dissolved Bring to 1 L with TC waterB5 STOCK #3 TC Water 750 mL Boric Acid 0.3 g Manganese Sulfate 1 g ZincSulfate Heptahydrate 0.2 g Potassium Iodide 0.075 g Sodium MolybdateDihydrate 0.025 g Cupric Sulfate (1 mg/mL) 2.5 mL Cobalt Chloride (1mg/mL) 2.5 mL Stir until completely dissolved Bring to 1 L with TC WaterB5 STOCK #4 TC Water 750 mL Myo-Inositol 10 g Nicotinic Acid 0.1 gPyridoxine, HCl 0.1 g Thiamine HCl 1 g Stir until completely dissolvedBring to 1 L with TC Water B5 STOCK #5 TC Water 750 mL Sequestrene 2.8 gStir until completely dissolved Bring to 1 L with TC Water

TABLE 12 WOODY PLANT MEDIUM (WPM) with 75 uM glyphosate as a selectionagent COMPOUND: Amount per liter WPM salt (Phytochem) 2.41 g Sucrose20.0 g Calcium Gluconate (Sigma) 1.29 g Clearys Fungicide (Carlin) 0.03g pH 5.6 AgarGel (Sigma) 4.0 g Autoclave Carbenicillin (40 mg/ml) 5.0 mlTicarcillin (100 mg/ml) 1.0 ml Cefotaxime (50 mg/ml) 4.0 ml Glyphosate(0.5M FS Stock) 0.15 ml

TABLE 13 BRM (BEAN ROOTING MEDIA) (for 4 L) MS Salts 8.6 g Myo-Inositol0.40 g Bean Rooting Media Vitamin Stock 8 mL L-Cysteine (10 mg/mL) 40 mLSucrose (Ultra Pure) 120 g pH 5.8 Washed Agar 32 g ADDITIONS AFTERAUTOCLAVING: BRM Hormone Stock 20.0 mL Ticarcillin/clavulanic acid 4.0mL (100 mg/mL Ticarcillin) BEAN ROOTING MEDIA VITAMIN STOCK(1 liter)Glycine 1.0 g Nicotinic Acid 0.25 g Pyridoxine HC1 0.25 g Thiamine HC10.05 g BRM Hormone Stock (Amount for 1 liter) 6.0 mL IAA (0.033 mg/mL)4.0 mL SDW

Example 9 High Throughput Single Seed Excision

The dry excision process may also be accomplished by use of asingulation system to provide individual (singulated) seeds forprocessing. After singulation the seed (e.g. a soybean seed) ismanipulated by a vacuum cup system to locate the seed. The seed is thenplaced between a set of vacuum cups and the seed is pinched between thecups, allowing removal of the seed coat by use of a blast of highpressure air alternatively a similar arrangement to pulse, sandblast, orair blast the seed coat from the seed. As shown in FIGS. 2-3, the seed(16) is placed on the lower vacuum cup (6) and the seed is pinched bylowering an upper vacuum cup (6). The seed and the two vacuum cups arethen rotated in opposite directions to produce a shearing force point orplane (5) along the center of the elliptical axis of the seed tofacilitate the splitting of the seed in the elliptical axis plane. Uponsplitting the upper vacuum cup is lifted, and/or one of the vacuumgenerators (8) is turned on, allowing manipulation of the explant andits separation from other portions of the seed. The explant may then bemoved to a desired location such as a tube or a well plate. In FIGS. 4-5a similar concept is executed, with the inclusion of a metal serratedsurface to help to rotate the seed without slipping. This systemincludes vacuum placement and pickup units. Although the explant maycomprise some cotyledonary tissue in addition to its embryonic tissue,it contains at least some of the meristematic region of the embryo suchthat typically the explant can produce a shoot within 12 weeks of theonset of tissue culture growth conditions.

The object of this process is to remove the meristematic tissue of theseed under dry conditions on a single seed high-speed basis and to thenplace the explant in a suitable container for additional transformationsteps. Additional explant processing (e.g. sterilization, culling orhydration) may also be performed between the removal of the explant fromthe seed and its delivery to the container. Additional processing couldalso include advance imaging of the explant for desirable traits andcharacteristics, sterilization and transformation treatments.Alternatively, seed could be imaged and sorted for viability andsuitability before going through the singulating and explant removalprocess. Such methods allowing for high throughput explant excision canbe made more efficient through parallel systems.

FIGS. 2-5 and 7-9 illustrate embodiments of mechanical separators andcleaner/sterilizers for use in excising transformable embryonic tissuefrom seed. FIGS. 2-5 illustrate mechanisms for holding a single seed asa shear force is applied, FIGS. 7-9 illustrate embodiments formechanically cleaning and sanitizing explant material using, forexample, an ion generator, charged plates to collect mold, dust, etc.;or UV germicidal lamps.

Referring now to FIGS. 2-5, which generally illustrate examples of amechanized apparatus for excising embryonic tissue from singulated seed(16), the singulated seed is held so as to apply a shear force asdescribed. In FIGS. 2-5, the first and second vacuum cups (6) and firstand second knurled posts (7) turn in opposite directions as a singleseed rests or is pinched against them, resulting in fracture of thesingulated seed. Other means for holding singulated seed, such asrollers or grates that allow application of an appropriate shear force,may also be employed.

Upon fracturing of the seed and excision of transformable embryonictissue, the explant comprising embryonic tissues (e.g. FIG. 1) may bemoved to a desired location or container for immediate use or storageunder appropriate conditions, for instance as described in Example 6above. This method for excising explant material from singulated seedallows automated high throughput preparation of convenient amounts oftransformable embryonic tissues.

Cleaning, culling, sterilization, and selection procedures may beapplied to non-excised seed in bulk, or following singulation, or theymay be applied to explant material following excision. FIGS. 7-9illustrate exemplary cleaner/sanitizers for performing such operationson explant material.

Example 10 Stacked Equipment for High-Throughput Explant Preparation

As shown in FIG. 10, the seeds are placed in the mechanized apparatus ontop (e.g. a Grainman® sheller; see Example 1) to be split as alsodescribed, for example, in Example 9 and in FIG. 6. Much of the lightmaterial, such as seed coats, are separated by aspiration during theexcision process, and the heavier seed fractions, such as cotyledonpieces and explants fall through for further separation of cotyledonsfrom other explant material. In this “stacked” configuration (FIGS.10-11), the heavier fraction now falls directly into an automaticseparator which separates the cotyledons from the explants, for instanceby size exclusion with vibrating mesh screens and gravity (e.g. asachieved by the CLIPPER OFFICE TESTER or similar component). Airflow mayalso be used to aspirate dust and other light seed debris away from thedesired material, to clean and/or to sterilize the material (e.g. FIGS.7-9: FIG. 11). These machines and processes are also describedindividually (e.g. Example 9), however their combination by stacking forcontinuous flow-through represents a further improvement in the processand apparatus.

Example 11 Transformation of Dry-Excised Soy Explants Stored forExtended Periods of Time

Dry-excised explants were stored for up to 20 months at −20° C. to 4°C., and then tested for survival, transformability and vigor. Explantsurvival and overall vigor appeared to be similar in all treatmentgroups, regardless of storage conditions or temperature compared tocontrol treatment (Treatment 1). This demonstrates the ability to storedry-excised explants for almost two years without detriment. Explantsfrom each treatment were tested for transient GUS expression 4 daysafter inoculation. Table 14 shows a comparison of meristem specific gusexpression between treatments, scored on a scale from 0-9, with 0 beingno visible expression, and 9 being extensive expression in all 3meristems of the embryo. This demonstrates that dry-excised explants cannot only survive long-term storage in various conditions withoutsignificant loss of vigor, but they also retain amenability totransformation. Thus it is now possible to excise large quantities ofexplants during off-peak times for later use, which representssignificant potential cost savings and flexibility in planning andexecuting transformation studies.

TABLE 14 Effect of storage duration and temperature on explanttransformation. Seed Transient gus Sterilization Excision StorageStorage expression Treatment Technique technique duration temperature(scale of 0-9) 1 & 2 50% bleach Automated dry None NA 0.90, 1.60 rinseexcision with Grainman Rice dehuller 3 50% bleach Automated dry 17months 4° C. 0.20 rinse excision with Grainman Rice dehuller 4 50%bleach Automated dry 17 months −20° C. 0.10 rinse excision with GrainmanRice dehuller 5 50% bleach Manual dry 20 months 4° C. 0.70 rinseexcision 6 50% bleach Manual dry 20 months −20° C. 1.50 rinse excision

Example 12 Identification of Suitable Pre-Inoculation Culture(“Pre-Culture”) Compositions and Conditions

It is likely that dry excised explants are still in a state ofsemi-dormancy when they are inoculated with Agrobacterium fortransformation. Thus a method was developed to stimulate the metabolicactivity of the dry excised explants prior to Agrobacterium inoculation,for increasing their transformation competency. That is, by manipulatingthe biology of the dry explant, it is possible to increase % germlinepositive events per explant by 2 to 10 fold.

Several media compositions: BGM (Table 10). INO (Table 11), or OR (Table15) were tested at 23° C. and/or 28° C. temperatures, and underdifferent light/dark conditions from 1 to 5 days, for their ability toenhance transformation competency. After pre-culturing step, explantswere pooled together and inoculated with the Agrobacterium cultureaccording to the method described in Example 5. Transient GUS expressionassays performed on explants showed increased GUS activity in thepre-cultured treatments after 2 days and 4 days of co-culture.

Plant losses occurred due to fungal infection in some of thepre-culturing experiments, but overall TF of the dry excised explantsthat were pre-cultured on filter papers wetted with BGM at 23° C. indark for 5 days appeared to be highest when compared with dry excisedexplants that were not pre-cultured. The losses due to fungalcontamination could be mitigated by using an anti-fungal agent such asBRAVO 75 and Captan 50 at about 1% each during the pre-culture and/orco-culture step. Southern blot and INVADER analysis of the plantsproduced in this example with a CP4 probe confirmed the transgenicnature of these plants.

TABLE 15 SOY Organogenic (OR) MEDIUM COMPOUND: PER 4 LITER: MS Salts17.2 g 3X Minor MS Salts 40 ml Nicotinic Acid (1 mg/ml) 4 ml PyridoxineHCl (1 mg/ml) 4 ml Thiamine HCl (1 mg/ml) 46.8 ml Sucrose (Ultra Pure)120 g Myo-Inositol (Cell Culture Grade) .40 g pH 5.8 Washed Agar 32 gADDITIONS AFTER AUTOCLAVING: Proline (2.5 m Stock) 19.2 ml TSG/ORHormone Stock 40.0 ml

TABLE 16 Effect of pre-culture of dry explant; transformation frequencyusing pMON10343. Pre-culture Media % Fungal Explant compositions Rootedloss Type and conditions Explants Shoots TF (Plantcons) WET None 300 155.00%  0% DRY None 650 6 0.92% 13% DRY BGM, 5 d 972 29 2.98%  0% 23°dark DRY BGM, 5 d 365 1 0.27% 44% 23° C. 16/8 light DRY BGM, 5 d 315 30.95%  7% 28° C. dark DRY BGM, 5 d 188 1 0.53% 62% 28° C. 16/8 light

Studies were repeated comparing two constructs, pMON101343, comprisingone T-DNA that comprises a CP4 gene specifying glyphosate resistance andan OriV replication origin: and pMON107350 comprising one T-DNA thatcomprises a CP4 gene specifying glyphosate resistance and an OriRreplication origin (e.g., see US20070074314) in the vector backbone.Again, pre-culturing of dry explants boosted TF as compared to the TF ofnon pre-cultured dry explants, as shown in Table 17.

TABLE 17 Additional studies on pre-culture of dry-excised explants.Explant type # Rooted and vector # Explants Shoots TF pMON101343 WET 53516 2.99% DRY 1331 8 0.60% DRY PRECULTURE 2437 43 1.76% pMON107350 WET671 11 1.64% DRY 190 0 0.00% DRY PRE-CULTURE 500 9 1.80%

As shown in Table 18, pre-cultured dry excised explants also yieldedhigher TFs when explants were cultured in liquid regeneration medium(media of Table 12 except for AgarGel) which was removed and addedautomatically using a robotic system. TF appeared to be even higher withthe liquid regeneration medium with a pre-culturing step. Wet excisedexplants in liquid media appear to have had low TF due to contamination.

Pre-culturing surprisingly improves competency for transformation andimproves transformation uniformity. Such improvements reduce variabilityduring production runs at industrial scale for producing transgenicsoybean plants and are likely to improve TFs where selection agents ingeneral yield lower TFs.

TABLE 18 Pre-culture of dry excised explants; comparison of solid andliquid media. Pre-culture Media Explant type compositions RegenerationEx- Rooted pMON101343 and conditions medium plants Shoots TF WET Nonesolid WPM 460 17 3.70% WET None liquid WPM 31 0 0.00% DRY None solid WPM1286 8 0.62% DRY None liquid WPM 128 0 0.00% DRY BGM, 5 d solid WPM 125733 2.63% 23° C. dark DRY BGM, 5 d liquid WPM 111 3 2.70% 23° C. dark

Example 13 Production of Transgenic Soybean Plants Using Dry SoybeanExplants and Spectinomycin Selection

Dry, viable, seeds (properly stored quality soybean seed compriseapproximately 10 to 12% internal moisture content) were rinsed withsterile water, or a solution of Sodium hypochlorite (ranging from 0 ppmto ˜30,000 ppm active chlorine, including 50 ppm and 200 ppm activechlorine) for 3 to 20 minutes. Liquid was then drained. This processraises the internal moisture content to approximately 16%. Followingthis brief surface sanitation step, the seed internal moisture contentwas lowered in a commercial seed dryer with a flow of dehumidified air(temperature controlled to approximately 60 to 90 degrees F.) to lessthan 8%.

Following desired storage, explants were hydrated for transformation.The types of media used for this step may be varied and included “beangermination medium” (BGM; Table 10), soy inoculum medium (INO; Table11), and prepared log-phase Agrobacterium growth cultures (AGRO). TheAgrobacterium growth culture was grown overnight in Lysogeny Broth (LB,also commonly referred to as Luria-Bertani Broth) to log phase, and thencentrifuged and resuspended to a final optical density at 660 nm of 0.25to 0.6. The medium used for the dilution is the same as the soy inoculummedium. Hydration temperatures and durations also can be varied, withsome experiments having explants that were soaked in one of thesesolutions overnight at 4° C. Other variations were made in the durationof exposure to respective hydration media, the various temperaturesduring this exposure, and the extent of saturation in the respectivemedia. Exposure times tested ranged from 0 to 24 hours. Hydrationsduring longer exposure times (those greater than 4 hours) were done ateither room temp (˜26° C.), 23° C., or 4° C. Exposure times of 4 hoursor less were all tested at room temperature. As an alternative tocompletely submerging or substantially saturating explants with liquidmedia during the hydration process, some treatments employed the use ofmoistened filter paper (enough liquid to wet, but not to saturate). Thiswas done with filter paper moistened with either BGM orAgrobacterium-culture medium. Hydration was performed in a variety ofvessels, including but not limited to conical centrifuge tubes,graduated glass bottles, or a PLANTCON tissue culture container (MPBiomedicals, Irvine, Calif.).

After hydration, explants were briefly sonicated in the presence of theappropriate Agrobacterium cultures. Co-culture and subsequent steps wereperformed in lighted Percival incubators for 2 to 5 days (16 hours oflight, 8 hours of dark, with light intensity of at least 5 μE to 200 μE)at a temperature of approximately 23 to 25° C., and may be performed upto about 35° C. Light is known to promote gene transfer fromAgrobacterium to plant cells. Spectinomycin was applied as a selectionagent either during hydration, in co-culture steps, and/or followingco-culture at 15 mg/L to 1000 mg/L.

Phenotype positive shoots (plants) were routinely recovered, as shown inTable 19, using the construct, pMON96999, comprising one T-DNAcomprising an aadA gene and an OriV origin of replication or theconstruct, or pMON101343 comprising one T-DNA comprising a CP4 gene andan OriV origin of replication. By “phenotype positive” in the presenceof spectinomycin, it is meant that shoots are green and robust, whilephenotype negative shoots are weak and bleached (white), if theyelongate at all. Spectinomycin or glyphosate were used in theregeneration medium (both solid or liquid) at the concentration shown inTable 19.

TABLE 19 Transformation frequency of dry soybean explants usingglyphosate or spectinomycin as selective agent. Spectinomycin (% TF)Glyphosate (% TF) 25 ppm 50 ppm 100 ppm 200 ppm 50 uM 4.66 4.24 6.345.99 2.00

Spectinomycin was also used as a selective agent for transformation ofdry excised soybean embryos utilizing the following conditions: 1 hrhydration in INO medium, 4 days co-culture in INO, 150 ppmspectinomycin, with culture on solid or liquid WPM (Table 12, with orwithout added agar). Temperatures of 23-25 or 28° C., up to about 35°C., may be utilized. Phenotype positive shoots were harvested at 8 and10 weeks post Agrobacterium inoculation, and rooting was induced onsolid BRM (Table 13) with 150 ppm Spectinomycin. Very hightransformation frequencies of 25.05% and 19.27% were obtained in twodifferent studies. Explants used in this study were not treated withcytokinin-like plant growth regulators (such as TDZ or BAP), thusdemonstrating that high transformation frequency could be achieved inthe absence of such plant growth regulators.

Example 14 Production of Transgenic Soybean Plants Using Dry SoybeanEmbryos, Spectinomycin, and Liquid Culture Medium

In these studies, explants were initially hydrated and eventuallyregenerated on WPM solid media with liquid overlay or WPM liquid mediumas above. All explants were transferred at 6 weeks post inoculation totrays containing Oasis® Wedge System (Smithers-Oasis USA; Kent, Ohio)and a simplified liquid medium (0.5 g/L WPM with 0.25 mg/L IBA). Rootedand shooted R₀ plants were obtained two to 4 weeks later. In all studiesand treatments, initial hydration of explants was done for 1 hour in therespective media as shown in the Table 20. Liquid culture medium was thesame as in Table 12 except glyphosate was replaced by spectinomycin at150 ppm. In liquid overlay treatment both solid and liquid culture mediawere used; liquid medium was dispensed over the top of explants as theywere lying on solid medium at a specified time during tissue culture asidentified in the Table 21. This was done as a type of media refreshmentand avoids the need for transferring explants from old media to newmedia. In the control treatments, explants were surface plated on asolid WPM medium (Table 12). Shoots were harvested and rooted on solidBRM as described above, except glyphosate was replaced withspectinomycin at 150 ppm.

TABLE 20 Transformation frequency with given hydration conditions. TF %Incubation with (mean of 3 Treatment Hydration medium Agrobacteriarepeats) 1- Control INO 0 minutes 3.10% 2 BGM w/o cefotaxime 0 minutes14.67% 3 BGM w/o cefotaxime 15 minutes 15.45% 4 BGM w/o cefotaxime 30minutes 18.50% 5 INO 0 minutes 13.98% 6 INO 15 minutes 9.64% 7 INO 30minutes 13.79%

TABLE 21 Liquid overlay timing. Liquid Liquid medium Oasis ® Wedge TF %overlay overlay volume transfer for (mean of Treatment timing on solidWPM regeneration repeats) Control- 1 NA None No 8.00% 2 None None Yes14.67% 3 3 weeks post 5 mLs Yes 15.45% inoculation 4 3 weeks post 10 mLsYes 18.50% inoculation 5 4 weeks post 5 mLs Yes 13.98% inoculation 6 4weeks post 10 mLs Yes 9.64% inoculation

Example 15 Production of Transgenic Soybean Plants Using Dry SoybeanEmbryos, Spectinomycin, and Transferring the Whole Regenerated Explantwith a Pre-Culturing Step

In these studies, as with Example 12, a pre-culturing step (5 days 23°C. dark in BGM) was used. A one hour hydration of the dry excisedexplant on INO medium was also done before the pre-culturing step. About12 mls of liquid WPM containing 150 ppm of spectinomycin was dispenseddirectly into the co-culture PLANTCON after the co-culture period, andexplants were surface plated on solid WPM containing 150 ppmspectinomycin 4 days later. In this example, phenotype positive greenshoots were identified at about week 4 of regeneration and transferredfrom WPM regeneration medium to trays containing Oasis® Wedge System(Smithers-Oasis USA; Kent, Ohio) and a simplified liquid medium (0.5 g/LWPM with 0.25 mg/L IBA). Rooted and shooted R₀ plants were obtained twoto 4 weeks later. Overall, pre-culturing in these studies also improvedTF % (Table 22). Percentage quality events shown below (Table 22) refersto the proportion of transgenic events demonstrating the presence of 1-2copies of both a gene of interest (GUS) and a marker gene (aadA) byInvader™ assay. Estimated marker-free TF (mTF) refers the % of eventswithout the marker gene. Explants used in this study were treated with1.0 ppm TDZ during co-culture, thus demonstrating that hightransformation frequency with dry explants could be achieved in thepresence of a cytokinin-like plant growth regulator, which could be usedin promoting shoot proliferation.

TABLE 22 Transformation frequency and quality observed from wholeregenerated explants. # % Estimated Protocol & # # Events Events qualitymTF vector type Explants produced TF % assayed events qTF % %** DryExcised - 260 34 13.1 +/− 0.17 32 21.9 2.7 +/− 0.23 0.62 2T/OriV DryExcised - 161 15 9.32 +/− 7.38 14 28.6 2.5 0.45 2T/OriRi Pre-cultured1641 319 19.4 +/− 5.42 311 24.4 4.6 +/− 1.35 1.1 Dry - 2T/OriVPre-cultured 336 66 19.64 +/− 1.97  64 20.3 3.9 +/− 1.22 0.7 Dry -2T/OriRi

Example 16 Production of Transgenic Soybean Plants Using Stored DrySoybean Embryos, Spectinomycin, and Transfer of Whole RegeneratedExplant with a Pre-Culturing Step

In this example, 3 months stored dry explants were used, and a 1 hrhydration step carried out in INO was utilized, on dry excised explants.Pre-culturing was performed for 5 days at 23° C. in dark conditions inBGM with 50 ppm nystatin and 10 ppm TBZ (thiabendazole) fungicides(nystatin and TZB Stock is made as by dissolving 50,000 ppm Nystatin and10,000 ppm TBZ in pure DMSO, diluted 1000 fold (1 ml of stock in 1L ofINO)). TDZ (1.0 ppm) and lipoic acid were both added to the inoculum andto the co-culture media (INO). The construct, pMON107379, was aconventional 2T vector comprising oriRi and aadA gene, and co-culturewas done for 5 days. After co-culture the explants were surface platedon solid WPM and then transferred to the Oasis® Wedge System(Smithers-Oasis USA; Kent, Ohio) with a simplified liquid medium (0.5g/L WPM with 0.25 mg/L IBA). As shown in Table 23, pre-culturing dryexplants boosted TF. Thus, 3 month old stored dry explants could performsimilarly to freshly excised dry explants. The addition to INOCo-culture media of nystatin (50 ppm) and thiabendazole (10 ppm)dissolved in DMSO (1.0 ml of DMSO per liter of INO) improved the healthof explants, likely by controlling yeasts and fungi commonly found inand on seeds and therefore can be beneficial when performing largeand/or automated tissue culture.

TABLE 23 Effect of pre-culture on TF (%) of stored dry explants. Explanttype Pre-culture step # Explants R0 plants TF Wet Excised No 263 7528.52% Stored Dry Explants No 678 71 10.47% Fresh Dry Explants No 375 246.40% Stored Dry Explants Yes 901 129 14.32% Fresh Dry Explants Yes 1008112 11.11%

All of the compositions and methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While the compositions and methods of this invention havebeen described in terms of the foregoing illustrative embodiments, itwill be apparent to those of skill in the art that variations, changes,modifications, and alterations may be applied to the composition,methods, and in the steps or in the sequence of steps of the methodsdescribed herein, without departing from the true concept, spirit, andscope of the invention. More specifically, it will be apparent thatcertain agents that are both chemically and physiologically related maybe substituted for the agents described herein while the same or similarresults would be achieved. All such similar substitutes andmodifications apparent to those skilled in the art are deemed to bewithin the spirit, scope, and concept of the invention as defined by theappended claims.

REFERENCES

The following references, to the extent that they provide exemplaryprocedural or other details supplementary to those set forth herein, arespecifically incorporated herein by reference.

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1. A method for transforming a plant comprising: (a) preparing anexplant from a plant seed under conditions wherein the explant does notgerminate and remains viable and competent for genetic transformation;wherein the explant comprises meristematic tissue, and wherein theexplant comprises an internal moisture content of from about 3% to about25%; and (b) transforming at least a first cell of the explant with aselected DNA.
 2. The method of claim 1, wherein the explant comprises asubstantially intact seed modified to expose at least a firsttransformable cell of the seed.
 3. The method of claim 1, wherein i) theseed is a mature seed; ii) the explant comprises an internal moisturecontent of from about 3% to about 20%; iii) said preparing the explantis carried out in the absence of a liquid; iv) the plant seed is asoybean, canola, corn, cotton, onion, peeper, tomato, cucurbit, rice, orwheat seed; v) said preparing the explant is automated; vi) said step(b) is carried out by bacterially-mediated transformation or particlebombardment; vii) the explant comprises an embryonic meristem; or viii)the explant comprises an internal moisture content of from about 4% toabout 16%. 4-6. (canceled)
 7. The method of claim 1, further comprising:(d) regenerating a transgenic plant from said cell of the explant,wherein the transgenic plant is stably transformed with the selectedDNA.
 8. The method of claim 1, further comprising i) storing the explantprior to step (b) under conditions wherein the explant does notgerminate and remains viable and competent for genetic transformation;ii) dehydrating said explant prior to step (b); iii) increasing themoisture content of the explant prior to or concurrently with step (b);iv) priming the plant seed and/or the explant prior to or concurrentlywith step (b); or v) dehydrating said plant seed prior to step (a).9-13. (canceled)
 14. The method of claim 8, wherein i) the explant isstored at a temperature of between about −80° C. and about 60° C.; ii)said method further comprises dehydrating said explant prior to step(b), wherein the explant is dehydrated prior to storing the explant;iii) storing the explant is carried out for from about 1 hour to about 2years; or iv) storing the explant is carried out for from about 1 hourto about 24 hours.
 15. (canceled)
 16. The method of claim 1, comprisingpreparing a plurality of explants from a plurality of seeds andselecting one or more explants exhibiting at least a firstcharacteristic indicative of the ability to transform the explant and/orregenerate a plant from the explant.
 17. The method of claim 16, whereinthe characteristic is selected from the group consisting of color, size,shape, density, proximate analysis, carbohydrate content, proteincontent, fat content, fibre (ash) content, moisture content, viability,germplasm, intactness, pathogen presence, and optical characteristics.18. (canceled)
 19. The method of claim 8, wherein priming the seedand/or the explant comprises contacting the seed with an aqueoussolution.
 20. The method of claim 19, wherein the aqueous solutioncomprises a disinfectant.
 21. The method of claim 20, wherein theaqueous solution comprises bleach or alcohol. 22-23. (canceled)
 24. Themethod of claim 3, wherein preparing the explant comprises an automatedprocess in which the plant seed is oriented as it passes through amechanical separator to provide a substantially uniform output ofregenerable meristematic plant tissue.
 25. (canceled)
 26. The method ofclaim 7, wherein the transgenic plant is regenerated without producing acallus tissue culture. 27-35. (canceled)
 36. A method for transforming aplant comprising: (a) obtaining an explant from a plant seed, whereinthe explant comprises meristematic tissue; (b) dehydrating the explant,wherein the explant after dehydrating does not germinate and remainsviable and competent for genetic transformation and comprises aninternal moisture content of from about 3% to about 25%; and (c)transforming at least a first cell of the explant with a selected DNA.37. The method of claim 36, further comprising the step of: (c)hydrating said explant prior to step (c).
 38. (canceled)
 39. The methodof claim 37, wherein hydrating said explant is performed under darkconditions. 40-48. (canceled)
 49. The method of claim 36, wherein i) theexplant after dehydrating comprises an internal moisture content of fromabout 3% to about 20%; ii) the explant after dehydrating comprises aninternal moisture content of or from about 4% to about 16%; iii) theplant seed is a soybean, canola, corn, cotton, onion, pepper, tomato,cucurbit, rice, or wheat seed; iv) preparing the explant is automated;or v) step (c) is carried out by bacterially-mediated transformation orparticle bombardment.
 50. (canceled)
 51. The method of claim 36, furthercomprising: (d) regenerating a transgenic plant from said cell of theexplant, wherein the transgenic plant is stably transformed with theselected DNA.
 52. The method of claim 51, wherein the transgenic plantis regenerated without producing a callus tissue culture.
 53. The methodof claim 36, further comprising i) storing the explant prior to step (c)under conditions wherein the explant does not germinate and remainsviable and competent for genetic transformation; ii) preparing aplurality of explants from a plurality of plant seeds and selecting oneor more explants exhibiting at least a first characteristic indicativeof the ability to transform the explant and/or regenerate a plant fromthe explant; or iii) priming the plant seed and/or the explant prior toor concurrently with step (c).
 54. The method of claim 53, wherein theexplant is stored at a temperature of between about −80° C. and about60° C.
 55. The method of claim 53, wherein storing the explant iscarried out for from about 1 hour to about 2 years or from about 1 hourto about 24 hours. 56-57. (canceled)
 58. The method of claim 53, whereinthe characteristic is selected from the group consisting of color, size,shape, density, proximate analysis, carbohydrate content, proteincontent, fat content, fibre (ash) content, moisture content, viability,germplasm, intactness, pathogen presence, and optical characteristics.59-62. (canceled)
 63. A method for producing a transformable planttissue comprising: (a) obtaining a regenerable explant from a plantseed, wherein the explant comprises meristematic tissue; and (b)dehydrating the explant to obtain a dried and regenerable explantcomprising an internal moisture content of from about 3% to about 25%.64. The method of claim 63, further comprising: (c) storing the driedand regenerable explant under conditions wherein the explant does notgerminate and remains viable and competent for genetic transformation.65. The method of claim 64, wherein storing the explant is carried outfor from about 1 hour to about 2 years or from about 1 hour to about 24hours.
 66. (canceled)
 67. The method of claim 63, wherein the dried andregenerable explant comprises an internal moisture content of from about3% to about 20% or from about 4% to about 16%.
 68. (canceled)
 69. Adried and regenerable explant competent for genetic transformationproduced by the method of claim 63.